1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor thin film making up a semiconductor device, such as memory and CPU (Central Processing Unit), a thin film transistor (TFT) made up of a same semiconductor thin film, and a method for manufacturing the same semiconductor thin film and the same TFT (and a manufacturing equipment being used in manufacturing the same semiconductor thin film.
2. Description of the Related Art
A conventional product manufactured by forming a semiconductor integrated circuit on a glass substrate is typified by a TFT. A conventional typical TFT is constructed, as shown in FIG. 17, by forming a channel region 103, a source region 104, a drain region 105, and an LDD (Lightly-doped drain) region 106 on a glass substrate 101 coated with a substrate coating layer 102, and then by forming a gate electrode 108 with a gate insulating film 107 being interposed between the gate electrode 108 and such the regions 103, 104, 105, and 106 as above, and by forming a contact hole in deposited silicon dioxide 109, and further by being wired using a metal 110.
A TFT being generally and presently used is classified depending on its active layer and a hydrogenated amorphous silicon TFT and poly-crystalline silicon TFT have come into wide use. A maximum temperature being employed in a process of fabricating the hydrogenated amorphous silicon TFT is about 300° C., which has achieved carrier mobility of about 1 cm2/Vsec. On the other hand, in the case of the poly-crystalline silicon TFT, by using, for example, a quartz substrate and by performing a high-temperature process of about 1000° C., a poly-crystalline silicon thin film having crystal grains being large in size is formed in which carrier mobility of about 30 to 100 cm2/Vsec has been achieved. However, the poly-crystalline silicon TFT has a disadvantage. That is, since the high-temperature process of about 1000° C. is performed when the poly-crystalline silicon is manufactured, a low-priced glass having a low-softening point cannot be used, unlike in the case of the hydrogenated amorphous silicon TFT.
To solve this problem, formation of a poly-crystalline thin film at low temperatures by using laser crystallization technology is being studied and developed. Laser crystallization technology is disclosed in, for example, Japanese Patent Publication No. Hei 7-118443 in which an amorphous silicon thin film (also being called an a-Si thin film) deposited on an amorphous substrate is crystallized by being irradiated with a short wavelength laser and which is applied to manufacturing of a TFT being excellent in a charge mobility characteristic. This laser crystallization technology has an advantage in that, since the technology enables crystallization of an amorphous silicon without elevating a temperature of an entire substrate, formation of a semiconductor device and/or a semiconductor integrated circuit on such a large-area substrate as a liquid crystal display or a like and such a low-priced substrate as glass or a like is made possible.
Moreover, a method is disclosed in Japanese Patent Application Laid-open Nos. Hei 11-64883 and 2000-306859 in which a poly-crystalline silicon thin film (also called poly-Si thin film) having crystal grains being larger in size is formed to manufacture a semiconductor thin film being excellent in a charge mobility characteristic.
For example, in the method disclosed in the Japanese Patent Application Laid-open No. Hei 11-64883, an amorphous silicon thin film is irradiated with an excimer laser beam to melt and re-crystallize it and to form a silicon crystal having grains being large in size. In the method disclosed in the Japanese Patent Application Laid-open No. 2000-306859, by irradiating an energy beam sequentially in a manner in which a location to be irradiated with the energy beam is shifted, a poly-crystalline semiconductor thin film is grown, that is, more specifically, while a laser is irradiated two or more times in a scanning manner in a region where the amorphous silicon thin film is melted and re-crystallized, the location to be irradiated with the laser is shifted in order to form a silicon thin film having crystal grains being large in size. In each embodiment disclosed in the Japanese Patent Application Laid-open No. Hei-64883, an aperture width (1 μm to 2 μm) is smaller than a width of a light-shielding mask pattern (1.5 μm to 5 μm) and an energy beam is irradiated through the aperture having the small width to melt the amorphous silicon thin film and the location to be irradiated with the laser is shifted to form a silicon thin film having crystal grains being large in size.
Furthermore, in the invention disclosed in the Japanese Patent Application Laid-open No. 2000-306859, as in the case of the invention disclosed in the Japanese Patent Application Laid-open No. Hei 11-64883, the amorphous silicon thin film is repeatedly irradiated with a laser while the region to be irradiated with the laser is shifted, little by little (for example, by 1 μm), within a range in which the amorphous silicon thin film is crystallized by one pulse irradiation with a laser. In the method employed in the above invention, a cyclical light and dark pattern in a light-shielded region is provided and a direction of crystallization is controlled by using a temperature gradient which changes depending on the light and dark pattern.
However, the technology disclosed in the Japanese Patent Application Laid-open No. Hei 11-64883 has a problem. That is, in the manufacturing method disclosed in the Japanese Patent Application Laid-open No. Hei 11-64883, the region where the amorphous silicon thin film is melt and re-crystallized is irradiated two or more times with a laser in a scanning manner and the location to be irradiated with the energy beam is shifted while being irradiated with the laser and, as a result, a difference between a width of a mask to intercept a laser and a width of an aperture to let the laser be transmitted is small, which causes much time to be taken in forming a silicon thin film having crystal grains being large in size.
Also, in the manufacturing method disclosed in the Japanese Patent Application Laid-open No. 2000-306859, while the amorphous silicon thin film is crystallized, the regions to be irradiated with a laser are sequentially shifted so that the regions irradiated with the laser are not overlapped to form the silicon thin film having crystal grains being large in size. However, since its movement distance is as short as about 1 μm, it takes much time to complete the processing in a specified region.